1. Field of the Invention
The present invention relates to a TFT (thin-film transistor) flat panel display device and its manufacturing method and, more particularly, to a TFT LCD (liquid crystal display) that greatly improves the brilliance.
2. Description of Related Art
In recent years, TFT liquid crystal display devices greatly attract consumer's attention because their advantages such as lighter weight and thinner size. Liquid crystal display devices (LCDs) have been accepted by consumers more and more since the improvement in manufacturing process and prices. However, conventional LCDs still have drawbacks, for example, poor brilliance. The brilliance of a conventional LCD results from many factors. It is well known that the phenomenon of shot mura is very important. This phenomenon of shot mura happens owing to the inevitable drawbacks happens in manufacturing process of the conventional LCDs. The phenomena of shot mura frequently results form the accuracy error of alignment and exposure. When using an exposure stepper to expose light on the panel substrate in lithographic process, the alignment error between the exposure stepper and the panel substrate in different exposure steps results in a different overlapped area. This error causes variation of capacitance of pixel functional components in different exposure areas on the same panel substrate; therefore different voltages applied to the pixel electrodes as the electrodes are conducted, and further result in variation of brilliance.
The phenomenon of shot mura can be understood from the following description with reference to FIG. 1. As illustrated in FIG. 1, Area A 110 and Area B 120 are two adjacent exposure areas in the display panel 100 ready for the application of exposure step of lithographic process. When stepper achieves exposure of former light exposure area (e.g. Area A 110) and shifts to next light exposure area (e.g. Area A 120), the alignment errors are reduced through the help of alignment machines and the existence of overlapping components around the periphery of former light exposure area (e.g. Area A 110). However, machine alignment cannot completely eliminate alignment errors. This alignment error causes a deviation between the pattern of the functional components (thin film transistors) 200 in Area A 110 (see FIG. 2A) and the pattern of the functional components (thin film transistors) 300 in Area A 120 (see FIG. 2B). For example, the overlapped area 360 between the drains 330 and gates 320 of all functional components 300 of Area B are relatively greater than the overlapped area 260 between the drains 230 and gates 220 of all functional components 200 of Area A due to alignment errors. The deviation can be estimated through calculating the changes which happened in the overlapped area 440 of the signal electrode 410 above the gate 420 (see FIG. 3) of the functional components of a LCD panel of prior arts and in the overlapped area 450 (a rectangular zone in most cases) of a drain electrode 430 above a gate 420 of those. Because the overlapped area between the drains 230 and the gates 220 in Area A and the overlapped area between the drains 330 and the gates 320 in Area B are different, a capacitance difference between the pixel functional components 200 of Area A and the pixel functional components 200 of Area B produced. When data signal voltage passed the functional components, the feed through voltage A obtained from data signal voltage passing through drains and gates to pixel electrodes of Area A is not equal to the feed through voltage B obtained from data signal voltage passing through drains and gates to pixel electrodes of Area B. Moreover, since the brilliance is dependent on the feed through voltage, this feed through voltage difference also results in different brilliance between Zone A and Zone B. This is the so-called phenomenon of shot mura, which lowers the display quality of the TFT LCD.
Therefore, it is desirable to provide a TFT LCD that eliminates the aforesaid drawbacks.